1. Field of the Invention
The present invention relates to an air filtering material for air cleaning capable of removing dust from air.
2. Description of the Related Art
JP-A No. Hei 11-156123 discloses an air cleaning device capable of collecting dust at a high collection efficiency. The air cleaning device has a coarse filter unit provided with a coarse air filtering material and a fine air filtering unit provided with a fine air filtering material in combination and is intended to filter dust at a high collection efficiency and to use the filtering materials for an extended period of time.
Filter paper as air filtering material catches dust particles in spaces between fibers. A nonwoven fabric of chemical fibers as air filtering material catches small dust particles by the agency of static electricity accumulated on the surfaces of the chemical fibers and catches large dust particles in spaces between the chemical fibers. Therefore, the spaces between the fibers must be miniaturized to improve cleaning efficiency, i.e., collection efficiency. However, the miniaturization of spaces between the fibers entails increase in the airflow resistance of the air filtering material and, when an air cleaner provided with such an air filtering material is placed in the intake system of an internal combustion engine, the air cleaner reduces the combustion efficiency of the internal combustion engine.
An air filtering material formed by oiling filter paper is capable of cleaning air at a high cleaning efficiency by the combined effect of catching dust particles in spaces between fibers and binding dust particles by the sticky oil. However, the airflow resistance of the filter paper cannot be reduced by expanding the spaces between the fibers of the filter paper because the oil is held in the minute spaces between the fibers of the filter paper by surface tension. It is difficult to hold an oil on a nonwoven fabric of chemical fibers because chemical fibers, in general, have smooth surfaces and the oil is unable to adhere easily to the surfaces of the chemical fibers.
The present invention has been made in view of those problems and it is therefore an object of the present invention to provide an air filtering material for air cleaning, capable of cleaning air at a high cleaning efficiency and at a low airflow resistance.
According to the present invention, an air filtering material for arresting dust from air that is caused to flow through the material, to thereby clean the air, comprises: a nonwoven fabric made of hollow chemical fibers each having therein a hole extending longitudinally thereof; each of the hollow chemical fibers having cracks and/or fissures defining minute clearances formed in an outer wall thereof so as to reach the longitudinal hole to thereby communicate the longitudinal hole with an exterior of the fiber; and an oil impregnated within the longitudinal hole, the cracks and fissures having a width on the order of a micronmeter or micrometers so that the oil within the longitudinal hole is caused to gradually exude through the cracks and fissures to the exterior of the fiber, whereby the dust is arrested by the exuding oil.
Therefore, large and small dust particles can be collected at a high collection efficiency by the combined effect of catching dust particles in spaces between the chemical fibers and binding dust particles by the oil even if the chemical fibers are distributed coarsely to reduce the air flow resistance of the air filtering material. The oil gradually exudes through the capillary cracks and/or fissures to wet the outer surfaces of the chemical fibers, so that dust particles can be bound by the oil wetting the surfaces of the chemical fibers, which further improves the cleaning efficiency of the air filtering material. Since the oil is caused to exude through the capillary cracks and/or fissures, the exudation of the oil is gradually effected and the oil continues to be adhered to the outer surfaces of the hollow fibers for a prolonged time, so that the air filtering operation can be maintained for a long time.